In recent years, with the increase of the resolution of solid-state imaging devices such as CCD (charge-coupled device) image sensors and CMOS (complementary metal-oxide-semiconductor) image sensors, the demand for information apparatus having a shooting function such as digital still cameras, digital video cameras, cellphones, and PDAs (personal digital assistants) has increased rapidly. Such information apparatus having a shooting function will be referred to as imaging apparatus.
To realize high-image-quality still image shooting in such imaging apparatus, it is necessary to increase the number of pixel cells. On the other hand, to realize high-image-quality moving image shooting, it is necessary to increase the rate of signal reading from an imaging device.
However, when the number of pixel cells is increased, the number of signals to be read out increases and hence it becomes difficult to increase the reading rate. That is, to realize both of high-image-quality still image shooting and high-image-quality moving image shooting, it is necessary to simultaneously attain mutually contradictory objectives, that is, increase of both of the number of pixel cells and the signal reading rate.
Among known driving methods of an imaging device for increasing the signal reading rate are what is called pixels summation reading in which output signals of plural pixel cells are added together in an imaging device and a resulting signal is output and decimation reading in which signal reading pixel cells are determined through decimation.
For example, Patent documents 1 and 2 disclose imaging apparatus using an imaging device which employs Bayer-arranged blocks each consisting of four (2×2) pixel cells having the same color. Reading is performed by adding together signals of the pixel cells of each block.